On 19 March this year, the tenth anniversary of George W Bush's declaration of war against Iraq, I was heading into Baghdad's ministry of the interior in search of an official from the inspector general's office who had been involved in the investigation into its purchase of fake bomb detectors.

Arriving at the entrance, a bomb – the first of 12 to explode in the city that day – detonated about a kilometre away.

The officer on the gate explained a few minutes later that just the day before two improvised explosive devices had been found nearby. He asked what we were doing at the ministry. He nodded as I explained. "We know that the detectors are useless," he replied bitterly. "They're fakes. We've seen it on the news."

The officer, however, remained last month in a minority in doubting the effectiveness of devices which some had nicknamed the Magic Wand.

At almost every checkpoint I passed through inside Baghdad during my three-week visit, the device was still visibly in use. Ironically on 19 March a Magic Wand was being used to scan our car as we drove into Karrada an hour or so later when there was another explosion in the distance, sending up a pall of black smoke from a car bomb that had detonated outside a restaurant near the Green Zone, where three people would be killed.

Visiting a checkpoint a few days before the wave of attacks I watched two police officers using the wands in the recommended fashion, halting in the road and shuffling their feet – supposed to build up static electricity – before approaching cars with the device held out.

But even as the trial was going on in London, officials in Iraq were still insisting that the devices worked.

"We know that a few of them are defective," said one official at the ministry of the interior who asked not to be named. "The other problem is how they are used. It requires the operator to be in the right frame of mind."

I hear other explanations both from policemen and ordinary Iraqis over why the wands are not reliable. Dental filings, aftershave, even toothpaste are blamed for false results.

What has been most damaging, a senior police official admits privately, is that officers have put their faith in the devices, relying on what is in effect no more than a dowsing rod in deciding which cars they should check, rather than using their own judgment.

The fact that the detectors were still in use as recently as last month is despite the fact that both Iraqi and US officials have known for two years that they are useless. Indeed, the Iraqi general who procured them through five corrupt and highly inflated contracts was arrested and jailed over his own part in the affair despite attempts by a former minister of the interior to grant him immunity from prosecution.

The issue was first raised in 2010 by Aqil al-Turehi, the inspector general of the ministry of interior's anti-fraud watchdog, who said then in a series of interviews that he had raised concerns that the bomb detectors did not work and had been purchased as part of a corrupt contract.

"There are strong indications of corruption in the deals to buy these explosives detectors and I submitted a report to that effect to the minister of interior and the parliamentary integrity commission," he said three years ago.

"Iraqis have paid a high price in blood for these fake bomb detectors," says the Iraqi MP Haneen Kado, who has raised the issue in the country's parliament.

"They are still being used everywhere and the Iraqi government has not taken the issue seriously.

"The problem is that there were people in the ministry of the interior who went in with [Jim] McCormick. I believe that there were officials who knew they weren't effective but still did the deal anyway. There is no transparency here. A lot of deals like this get done like this because there is so much corruption.